The present invention relates to jitter analysis.
Characterization of the transient behavior of e.g. high-speed digital circuits, i.e. the transition of a digital signal from one logical state/level to another logical state/level, has become growingly important for designing as well as manufacturing such digital circuits. With a continuously increasing level of SOC (system on a chip) integration multiple transistors switch at the same time thereby disadvantageously influencing timing characteristics of the signals generated by means of switching noise. Further, electrical fields generated by nearby clock distribution lines, etc. can also cause timing instabilities such as jitter. Accordingly, an amount of jitter that can be tolerated or that characterizes the transmission quality, e.g., of an IO-device is used as a figure of merit in specifications or standardizations.
ITU-T G.701 defines jitter as short-term non-cumulative variations of the significant instants of a digital signal from their ideal positions in time. The significant instant can be any convenient, easily identifiable point on the signal such as the rising or falling edge of a pulse or the sampling instant. By plotting the relative displacement of the instants within a real pulse train that has some timing jitter with respect to an ideal pulse train, the so-called jitter time function can be obtained. Alternatively, the jitter spectrum can be displayed in the frequency domain in order to provide jitter analysis. In a probabilistic approach jitter-histograms showing the likelihood for a transition can be established and analyzed.
In order to characterize devices with respect to jitter semiconductor manufacturers expect to use measurement equipment that is able to separate different types of jitter in order to allow an identification of sources of error and to provide further improvements of product quality. In particular, it is generally desirable to separate random jitter (RJ) from deterministic jitter (DJ). However, existing techniques such as that disclosed, e.g., in Li, M. P., Wilstrup, J., Jessen, R., Petrich, D. in: “A New Method for Jitter Decomposition through its Distribution Tail Fitting”, Proc. Intl. Test Conf., pp. 788–794 (1999) are very time consuming, need many measurements to be taken per data point and therefore do not meet the requirements of high volume production.